The Paleo-Indian Clovis people, the earliest known settlers of Arizona, arrived in the State at least 12,000 years ago near the end of the Pleistocene period (the Ice Age). The climate was cooler and wetter than the present, and Arizona was populated by huge animals such as mammoths. Subsisting on hunted and gathered resources, the people used distinctive spear points to hunt these animals. By 6,000 B.C., warmer and drier climatic conditions contributed to the extinction of the Pleistocene megafauna, and the people changed their way of life.

Those who lived in Arizona after the Paleo-Indians are called the Archaic people. They subsisted on a wide variety of plant and animal foods, moving frequently over the landscape to hunt and gather the resources available in different places during different seasons. Widespread styles of projectile points indicate that the Archaic people had wide-ranging social and trade networks. Late in the Archaic period, Archaic groups began to plant selected crops, most notably corn, and many became less mobile and began to inhabit settlements for longer periods of time. People adopted the practice of farming at different times, and with varying degrees of reliance, in different regions of Arizona. Even those who came to rely to the greatest degree on farming continued to obtain a substantial proportion of their diet from hunted and gathered foods.

By 2,000 years ago, many people had settled into villages and relied on stored foods during the winter. During this Formative period, they began to make and use pottery and to develop different techniques of agriculture such as canal irrigation. Gradually, larger villages were built and different groups of people began to emerge. The Hohokam, who inhabited the deserts of southern Arizona, constructed large networks of irrigation canals along the rivers. The Mogollon people lived in the mountains and valleys of eastern Arizona, and ancestral Puebloan peoples lived in the Colorado Plateau and Arizona Strip regions. The Patayan inhabited the Colorado River and desert areas of western Arizona. Each of these cultures had distinctive pottery and architectural styles. However, throughout Arizona, there were variations within each of these groups, as local populations adapted to local environmental conditions and social networks. The people in all parts of Arizona participated in trade networks and maintained contact with their neighbors in Mexico. Trade items included shell from the Gulf of California and the Pacific, turquoise from the Southwest, and copper bells and parrots from Mexico.

Around A.D. 1100, many groups began to construct structures such as multi-room pueblos, more substantial than the pithouses and brush shelters used up to that time. Some societies, notably among the Hohokam and ancestral Puebloans, achieved greater degrees of social and political complexity, possibly based on individual differences in wealth, social status and political influence. These groups constructed towns that housed hundreds or even thousands of people. Late in the prehistoric period, changes in environmental conditions, social networks, or population size may have contributed to resource shortages and conflict. Many groups abandoned such areas as valleys and aggregated into larger, more defensible settlements in upland areas or remote canyons. Such settlements included pueblos on Perry Mesa that are now managed within the Agua Fria National Monument. There is evidence of warfare during this period. By A.D. 1450, many of these large settlements and some geographic areas were apparently abandoned as groups migrated to other regions such as the area now inhabited by the Hopi Tribe. It is possible that in some areas, people reverted to less intensive and more mobile subsistence practices and smaller settlements. Diseases introduced later by European immigrants may have caused dramatic declines in native populations.

Many modern tribes, including the Hopi and the O'odham, may be the descendants of the ancestral Puebloans, Mogollon and Hohokam. Archaeological and linguistic evidence indicate that other groups such as the Navajo, Apache and Paiute were later immigrants to Arizona, arriving sometime before the fifteenth century.

The Spanish arrived in Arizona in 1540 when the expedition of Francisco Vasquez de Coronado made its way north along the San Pedro River en route to Zuni. Other Spaniards followed, accompanied by missionaries sent by the Spanish Crown to pacify the native populations. Father Eusebio Francisco Kino traveled extensively between the San Pedro and Gila Rivers between 1691 and 1702, establishing missions and introducing European livestock and crops to the Indian rancherias. In 1775, Captain Juan Bautista de Anza led a colony of settlers to California along the Santa Cruz and Gila Rivers, passing by Painted Rocks. Anza's route is now a designated Millennium Trail managed in part by the BLM. On the eve of American Independence in 1776, Fathers Silvestre Velez de Escalante and Francisco Atanasio Dominguez were the first Europeans to traverse the Arizona Strip. That same year, construction began on the Presidio of Santa Cruz de Terrenate, now managed by BLM, to guard the northern border of New Spain.

In the mid-1820's, Anglo-American fur trappers, known as "mountain men," entered Arizona and began trapping the Gila River. One of the most famous was Jedediah Smith, who traveled down the Virgin River through the Arizona Strip, then down along the Colorado. Another was Kit Carson who was later hired to guide the U.S. Army. After the United States acquired what is now Arizona through the war with Mexico in 1848 and the Gadsden Purchase in 1854, another "army" of American explorers and surveyors descended on the Territory to survey the international boundary, mark wagon roads, scout possible routes for a transcontinental railroad, and determine the limits of navigation on the Colorado. The Butterfield Overland Mail stage began semiweekly service across Arizona in 1858, its route still traceable on BLM lands. The incursions of whites were understandably not welcomed by the Indians, and an average of twenty-one skirmishes between Indians and whites occurred each year from 1866 to 1875. Approximately three dozen military camps and forts were established and used in Arizona between 1865 and 1920.

Ranching has been an important part of Arizona's history since the 17th century when Spanish missionaries introduced cattle. Large Spanish, and later Mexican, land grant ranches operated in the southern part of the State. Two 1827 Mexican land grants, the San Juan de las Boquillas y Nogales grant and the San Rafael del Valle grant, were later acquired by the BLM and designated by Congress as the San Pedro Riparian National Conservation Area. One of the most important ranches at the end of the 19th century was Walter Vail's Empire Ranch, controlling nearly a thousand square miles of range stretching from the Mexican border to the Rincon Mountains. Its adobe headquarters remain today as one of BLM's most important historic properties.

After the gold rush waned in California, miners came east to prospect in Arizona, finding rich strikes of silver and gold. Boom times began, bringing more people to the Territory. The population of Arizona doubled between 1860 and 1864, then doubled again by 1870. By 1880, one out of five male workers in the Territory was a miner. Silver dominated production in the beginning, but by 1888, copper took its place as the mainstay of Arizona's economy. Settlement followed the development of mineral deposits, bringing residents and towns to Arizona's southern, central and western deserts. Copper mining has continued to play a vital role in the State's history. By 1981, Arizona ranked first among the United States in production of copper.